Photonic systems use a combination of radio-frequency (RF) technology and optical technology to transport signals, and can be used for an opto-electronic oscillator (OEO). The oscillator uses the light energy to produce pure microwave signals. A typical oscillator comprises an optical modulator that is supplied with light from a low-noise laser source, a delay fiber, and a light detector. The detector forms an electrical signal that is amplified and filtered, and then is used to control the modulator. The modulator encodes or modulates the light from the light source with the electrical signal. The modulated light is then passed through the delay fiber, which introduces a delay in the light, and is then provided to the light detector. The light detector then converts the received light into the electrical signal that is used provided to the optical modulator.
The frequency at which the OEO oscillates can be controlled by placing a frequency selective element within the electronic portion of the loop. Also, the frequency at which the OEO oscillates can be controlled by placing a frequency selective element within the optical portion of the loop. For further information see “Optoelectronic Oscillator for Photonic Systems, Yao, X. S. et al, IEEE Journal of Quantum Electronics, Vol. 32, No. 7, July 1996, pgs 1141-1149, which is hereby incorporated herein by reference.